Generally, step units are arranged on vehicles so as to make it easy for a user to enter or leave the vehicle. Step units are more particularly useful for vehicles having high ground clearance, e.g. rotorcraft.
Document GB 15077 discloses a first step unit that is partially foldable.
That first step unit comprises a main block provided with a plurality of steps, the main block having first and second bottom steps hinged thereto.
A rod is then secured to the bottom face of the second bottom step. By using a lever, a user then moves the rod so as to fold the first and second bottom steps under the main block.
That first step unit is thus partially foldable, the first and second bottom steps being stored under the main block. However the main block is neither folded nor retracted.
Consequently, it is not possible to enter the step unit into a housing.
However, on rotorcraft, step units are preferably arranged in the bottom space of the fuselage known as the “subfloor structure” to the person skilled in the art. The subfloor structure is then of rounded shape at its ends, which ends are sometimes known as “hull quarters”.
In flight, in order to avoid degrading the aerodynamic capacities of the rotorcraft, the step unit is contained completely within a housing situated in the subfloor structure. In general, the housing is arranged mostly within the subfloor structure, but it might possibly project a little therefrom, e.g. because of the presence of cables or pipework.
On the ground, the step unit is deployed and projects from its housing.
Consequently, the first step unit of document GP 15077 is not suitable for rotorcraft insofar as the main block cannot be folded, nor even retracted.
In contrast, document U.S. Pat. No. 5,584,493 discloses a second step unit comprising a single block provided with a plurality of steps.
Since that block is retractable, it can be extended or retracted into a housing with the help of a system that is controlled by pressurized fluid.
Nevertheless, that step unit is relatively bulky insofar as it is merely retractable. The block provided with the step is not itself foldable, so it is not possible to reduce its overall size in order to enter into a housing that is small.
Although effective, the second step unit described in document U.S. Pat. No. 5,584,493 is unsuitable for being arranged on a rotorcraft because of its dimensions, the space available in the “hull quarter” of the subfloor structure of a rotorcraft unfortunately being restricted by its very nature.
Finally, document EP 0 884 218 describes a third step unit.
That third step unit includes a single foldable step, the step passing from an active extended position to an inactive retracted position as a function of moving a door of the vehicle that is fitted with the third step unit.
The third step unit is dedicated specifically to an automobile application.
The third step unit has only one step, which might not be sufficient for a vehicle having relatively high ground clearance.
Furthermore, it can be seen that the step remains outside the vehicle in all of its positions.
Such a configuration would seem to be unsuitable for an aviation application. It can readily be understood that the forces exerted by air on the step would then be sufficient to damage the step unit, e.g. by causing untimely deployment of the step.